1. Field of the Invention
The present invention generally relates to an electric power generating device for vehicles. More particularly, the present invention relates to an electric power generating device for charging a battery for vehicles by using an induction machine.
2. Related Arts
In the Japanese Unexamined Patent Publication (KOKAI) No. 63-302119, an induction type electric power generating device, which is driven by an exhaust gas turbine for vehicles, is disclosed. This induction type electric power generating device aims to give priority to the efficiency of the turbine and therefore operates within the rotation area of the best turbine efficiency by adjusting the slip thereof.
In the Japanese Unexamined Patent Publication (KOKAI) No. 2-87999, there is a proposal that the required slip state should be maintained by controlling the frequency of the inverter based on the revolution number (RPM) of the electric power generating device detected by an RPM sensor.
In the induction type electric power generating device proposed in the above publications, the electric power generating amount should be adjusted by detecting the RPM of the device and controlling the slip. However, in induction type electric power generating devices, unlike synchronous electric power generating devices, the exciting frequency is determined from the charging power source side. Characteristically, the torque, or the electric power generating amount significantly varies due to even slight change in the RPM (slip) in spite of the frequent, speedy speed variation of the slip caused by the variation of the engine RPM. Therefore, when an induction machine is applied to an electric power generating device for vehicles, there is a need to use a high-precision, high-responsive RPM sensor (speed sensor) to control the slip at a high speed and a high precision. This has been a major drawback of a conventional 3-phase synchronous electric power generating devices (alternators) in using induction type electric power generating devices as electric power generating devices for vehicles.
In particular, the above problem in controlling electric power generation by controlling the slip is more serious when the induction type electric power generating device is speed-increasingly driven by a belt for reducing the size and weight thereof or provided with multiple poles (8 poles or so) for increasing the frequency and speed.